import { Injectable, ConflictException, NotFoundException, BadRequestException, Logger } from '@nestjs/common';
import { PrismaService } from '../../common/prisma.service';
import { HoldSeatsDto, JourneyDirection } from './seats.dto';
import { Cron, CronExpression } from '@nestjs/schedule';
import { SegmentsService } from '../segments/segments.service';
import { SystemConfigService, CONFIG_KEYS } from '../system-config/system-config.service';
import { AuditService } from '../../common/audit.service';
import { computePaymentDeadline } from '../../common/utils/payment-deadline.utils';

@Injectable()
export class SeatsService {
  private readonly logger = new Logger(SeatsService.name);

  constructor(
    private prisma: PrismaService,
    private segmentsService: SegmentsService,
    private systemConfig: SystemConfigService,
    private auditService: AuditService,
  ) {}

  async getSeatMap(scheduleId: string, coachTypeId?: string, journeyDirection?: JourneyDirection, originStationId?: string, destinationStationId?: string) {
    const schedule = await this.prisma.trainSchedule.findUnique({
      where: { id: scheduleId },
      select: { originStationId: true, destinationStationId: true },
    });
    if (!schedule) throw new NotFoundException('Schedule not found');

    const assignments = await this.prisma.coachAssignment.findMany({
      where: {
        scheduleId,
        ...(coachTypeId ? { coach: { coachTypeId } } : {}),
      },
      include: {
        coach: {
          include: {
            seats: { orderBy: [{ row: 'asc' }, { col: 'asc' }] },
            coachType: { include: { seatClasses: true } },
          },
        },
      },
      orderBy: { positionNumber: 'asc' },
    });

    const allSeatIds = assignments.flatMap((a: any) => a.coach.seats.map((s: any) => s.id));
    const effectiveStatuses = await this.resolveEffectiveStatuses(
      scheduleId, 
      allSeatIds, 
      originStationId ?? schedule.originStationId, 
      destinationStationId ?? schedule.destinationStationId,
      journeyDirection
    );

    return {
      coaches: assignments.map((a) => {
        const allSeats   = a.coach.seats;
        const coachTypeName = a.coach.coachType?.name ?? '';
        const seatClassNames = a.coach.coachType.seatClasses.map((sc: any) => sc.name);
        const isBedCoach = this.isBedCoach(coachTypeName);
        // Compute actual beds-per-room from first room to correctly identify VIP (4) vs Economy (6)
        const bedsPerRoom = isBedCoach
          ? allSeats.filter((s: any) => s.row === (allSeats[0] as any)?.row).length
          : 0;
        const bedCategory = isBedCoach ? this.getBedCategory(coachTypeName, bedsPerRoom) : null;

        const mappedSeats = allSeats.map((s: any) => {
          const resolvedBedPosition = isBedCoach
            ? this.resolveBedPosition(s.col, s.bedPosition)
            : s.bedPosition;
          const effectiveStatus = effectiveStatuses.get(s.id) ?? (s.status === 'BLOCKED' || s.status === 'BOOKED' ? s.status : 'AVAILABLE');
          return {
            id:          s.id,
            seatNumber:  s.seatNumber,
            label:       s.seatNumber,
            status:      effectiveStatus,
            kind:        s.kind,
            row:         s.row,
            col:         s.col,
            isWindow:    s.isWindow,
            isAisle:     s.isAisle,
            bedPosition: resolvedBedPosition,
            // Bed-specific fields (only when coach is a bed coach)
            ...(isBedCoach ? {
              room_id:  `${a.coach.id}-R${s.row}`,
              category: bedCategory,
              position: this.colToPosition(s.col, a.coach.arrangement),
              bed_type: this.bedPositionToType(resolvedBedPosition),
            } : {}),
          };
        });

        const base = {
          id:             a.coach.id,
          assignmentId:   a.id,
          coachNumber:    a.coach.number,
          label:          a.coach.number,
          mode:           a.coach.status,
          name:           `Coach ${a.coach.number}`,
          coachTypeId:    a.coach.coachType?.id ?? null,
          coachTypeName,
          isBedCoach,
          bedCategory,
          seatClasses:    seatClassNames,
          seatClass:      seatClassNames.length > 0 ? seatClassNames[0] : 'Standard',
          positionNumber: a.positionNumber,
          seatArrangement: a.coach.arrangement,
          totalSeats:     a.coach.capacity,
        };

        if (isBedCoach) {
          // Group seats into rooms; row = room number
          const roomMap = new Map<number, any[]>();
          for (const seat of mappedSeats) {
            if (!roomMap.has(seat.row)) roomMap.set(seat.row, []);
            roomMap.get(seat.row)!.push(seat);
          }
          const rooms = Array.from(roomMap.entries())
            .sort(([a], [b]) => a - b)
            .map(([roomNumber, beds]) => ({
              room_id:    `${a.coach.id}-R${roomNumber}`,
              roomNumber,
              category:   bedCategory,
              totalBeds:  beds.length,
              beds,
            }));
          return { ...base, rooms, seats: mappedSeats };
        }

        return { ...base, seats: mappedSeats };
      }),
    };
  }

  private isBedCoach(coachTypeName: string): boolean {
    const n = coachTypeName.toLowerCase();
    return n.includes('bed') || n.includes('berth') || n.includes('sleeper') || n.includes('couchette');
  }

  private getBedCategory(coachTypeName: string, bedsPerRoom?: number): 'ECONOMY_BED' | 'VIP_BED' {
    const n = coachTypeName.toLowerCase();
    // Explicit VIP name check first
    if (n.includes('vip')) return 'VIP_BED';
    // Fall back to actual beds-per-room count: 4 = VIP, 6 = Economy
    if (bedsPerRoom === 4) return 'VIP_BED';
    return 'ECONOMY_BED';
  }

  // col format: L1, L2, L3, R1, R2, R3  (new)  or  A, B, C, D  (legacy)
  // arrangement e.g. "2+2", "3+3", "2+0" → "leftCount+rightCount"
  private colToPosition(col: string, arrangement?: string): 'LEFT' | 'RIGHT' | null {
    if (!col) return null;
    // New named-col format: L1, L2, R1, R2 …
    if (/^L\d+$/.test(col)) return 'LEFT';
    if (/^R\d+$/.test(col)) return 'RIGHT';
    // Legacy single-letter cols (A, B, C, D …): derive from arrangement
    const colIndex = col.toUpperCase().charCodeAt(0) - 65; // A=0, B=1, C=2 …
    if (arrangement) {
      const [leftStr, rightStr] = arrangement.split('+');
      const rightCount = parseInt(rightStr ?? '0', 10);
      if (rightCount === 0) return 'LEFT'; // single-side berth coach — all LEFT
      const leftCount = parseInt(leftStr, 10) || 0;
      return colIndex < leftCount ? 'LEFT' : 'RIGHT';
    }
    return 'LEFT'; // safe default when no arrangement info
  }

  private bedPositionToType(bedPosition: string | null): 'LOWER' | 'MIDDLE' | 'UPPER' | null {
    if (!bedPosition) return null;
    const map: Record<string, 'LOWER' | 'MIDDLE' | 'UPPER'> = {
      lower: 'LOWER', middle: 'MIDDLE', upper: 'UPPER',
    };
    return map[bedPosition.toLowerCase()] ?? null;
  }

  // Derives bedPosition from col when the seat was created with legacy A/B/C columns
  // (new coaches use L1/L2/L3/R1/R2/R3 and store bedPosition explicitly).
  // Col-to-tier mapping: A → lower, B → middle, C → upper, D → upper (4-tier).
  private resolveBedPosition(col: string, storedBedPosition: string | null): string | null {
    if (storedBedPosition) return storedBedPosition;
    const legacyMap: Record<string, string> = { A: 'lower', B: 'middle', C: 'upper', D: 'upper' };
    // Also handle numeric suffix in L/R cols: L1→lower, L2→middle, L3→upper
    if (/^[LR]\d+$/.test(col)) {
      const tier = parseInt(col.slice(1), 10);
      if (tier === 1) return 'lower';
      if (tier === 2) return 'middle';
      return 'upper';
    }
    return legacyMap[col?.toUpperCase()] ?? null;
  }

  async resolveEffectiveStatuses(
    scheduleId: string,
    seatIds: string[],
    originStationId?: string,
    destinationStationId?: string,
    journeyDirection?: JourneyDirection,
  ): Promise<Map<string, string>> {
    const statusMap = new Map<string, string>();
    if (seatIds.length === 0) return statusMap;

    // Resolve the requested leg's sequence range once
    let reqFrom: number | undefined;
    let reqTo: number | undefined;
    let allStopTimes: { stationId: string; sequence: number }[] | null = null;

    const getStopTimes = async () => {
      if (!allStopTimes) {
        allStopTimes = await this.prisma.tripStopTime.findMany({
          where: { scheduleId },
          select: { stationId: true, sequence: true },
        });
      }
      return allStopTimes;
    };

    if (originStationId && destinationStationId) {
      const stops = await getStopTimes();
      const seqOf = (id: string) => stops.find(s => s.stationId === id)?.sequence;
      reqFrom = seqOf(originStationId);
      reqTo   = seqOf(destinationStationId);
    }

    // ── Active holds ──────────────────────────────────────────────────────────
    const activeHolds = await this.prisma.seatHold.findMany({
      where: { scheduleId, expiresAt: { gt: new Date() }, seatIds: { hasSome: seatIds } },
      select: { seatIds: true, createdBy: true },
    });

    const reqDirection = journeyDirection || JourneyDirection.ONE_WAY;

    for (const hold of activeHolds) {
      let holdFrom: number | undefined;
      let holdTo: number | undefined;
      let holdDirection = JourneyDirection.ONE_WAY;
      
      try {
        if (hold.createdBy?.trimStart().startsWith('{')) {
          const meta = JSON.parse(hold.createdBy);
          const stops = await getStopTimes();
          const seqOf = (id: string) => stops.find(s => s.stationId === id)?.sequence;
          holdFrom = seqOf(meta.originStationId);
          holdTo   = seqOf(meta.destinationStationId);
          holdDirection = meta.journeyDirection || JourneyDirection.ONE_WAY;
        }
      } catch { /* ignore */ }

      for (const seatId of hold.seatIds) {
        if (!seatIds.includes(seatId)) continue;
        
        // Check leg overlap
        const legsOverlap = 
          reqFrom === undefined || reqTo === undefined || 
          holdFrom === undefined || holdTo === undefined ||
          (holdFrom < reqTo && reqFrom < holdTo);
        
        // Check direction conflict
        const directionsConflict = this.checkDirectionConflict(reqDirection, holdDirection);

        if (!legsOverlap || !directionsConflict) {
          // This hold does not conflict with the requested leg/direction.
          // Explicitly mark AVAILABLE so the DB's HELD status (set by the
          // opposing-direction hold) does not bleed through via the fallback.
          if (!statusMap.has(seatId)) statusMap.set(seatId, 'AVAILABLE');
          continue;
        }
        
        statusMap.set(seatId, 'HELD');
      }
    }

    // ── Confirmed bookings via JourneySegment ─────────────────────────────────
    const bookedSegments = await this.prisma.journeySegment.findMany({
      where: {
        scheduleId,
        seatId: { in: seatIds },
        journey: { status: { in: ['CONFIRMED', 'PENDING_PAYMENT'] } },
      },
      select: { seatId: true, departureStationId: true, arrivalStationId: true },
    });

    if (reqFrom !== undefined && reqTo !== undefined) {
      const stops = await getStopTimes();
      const seqOf = (id: string) => stops.find(s => s.stationId === id)?.sequence;
      for (const seg of bookedSegments) {
        if (!seg.seatId) continue;
        const segFrom = seqOf(seg.departureStationId);
        const segTo   = seqOf(seg.arrivalStationId);
        if (segFrom !== undefined && segTo !== undefined) {
          if (segFrom < reqTo && reqFrom < segTo) statusMap.set(seg.seatId, 'BOOKED');
        } else {
          statusMap.set(seg.seatId, 'BOOKED');
        }
      }
    } else {
      for (const seg of bookedSegments) {
        if (seg.seatId) statusMap.set(seg.seatId, 'BOOKED');
      }
    }

    return statusMap;
  }

  /**
   * Check if two journey directions conflict (should not be allowed simultaneously)
   * For round-trip bookings: OUTBOUND and RETURN should NOT conflict on same schedule
   */
  private checkDirectionConflict(current: JourneyDirection, existing: JourneyDirection): boolean {
    // OUTBOUND and RETURN are allowed simultaneously (round-trip on different schedules)
    if ((current === JourneyDirection.OUTBOUND && existing === JourneyDirection.RETURN) ||
        (current === JourneyDirection.RETURN && existing === JourneyDirection.OUTBOUND)) {
      return false;
    }
    
    // Same directions conflict (e.g., two OUTBOUND or two RETURN bookings)
    if (current === existing) {
      return true;
    }
    
    // ONE_WAY conflicts with other ONE_WAY bookings only
    if (current === JourneyDirection.ONE_WAY && existing === JourneyDirection.ONE_WAY) {
      return true;
    }
    
    // ONE_WAY with OUTBOUND/RETURN: conflict (to maintain safety for legacy bookings)
    if (current === JourneyDirection.ONE_WAY || existing === JourneyDirection.ONE_WAY) {
      return true;
    }
    
    // Default: no conflict
    return false;
  }

  async holdSeats(dto: HoldSeatsDto) {
    const passengerIds = dto.passengers.map(p => p.passengerId);
    const seatIds      = dto.passengers.map(p => p.seatId);

    if (new Set(passengerIds).size !== passengerIds.length)
      throw new BadRequestException('Duplicate passengerId in passengers list');
    if (new Set(seatIds).size !== seatIds.length)
      throw new BadRequestException('Duplicate seatId in passengers list');

    const [holdMinutes, cutoffHours] = await Promise.all([
      this.systemConfig.getNumber(CONFIG_KEYS.SEAT_HOLD_DURATION_MINUTES),
      this.systemConfig.getNumber(CONFIG_KEYS.HOLD_CUTOFF_HOURS_BEFORE_DEPARTURE),
    ]);
    const expiresAt = new Date(Date.now() + holdMinutes * 60 * 1000);

    const schedule = await this.prisma.trainSchedule.findUnique({
      where: { id: dto.scheduleId },
      select: { departureAt: true },
    });
    if (!schedule) throw new NotFoundException('Schedule not found');

    const msUntilDeparture = schedule.departureAt.getTime() - Date.now();
    const cutoffMs = cutoffHours * 60 * 60 * 1000;
    if (msUntilDeparture <= cutoffMs) {
      throw new BadRequestException(
        `Seats cannot be held within ${cutoffHours} hour${cutoffHours !== 1 ? 's' : ''} of departure`,
      );
    }

    const hold = await this.prisma.$transaction(async (tx) => {
      const seats = await tx.seat.findMany({
        where: { id: { in: seatIds } },
        select: { id: true, status: true, seatNumber: true },
      });

      if (seats.length !== seatIds.length) {
        const found = new Set(seats.map(s => s.id));
        const missing = seatIds.filter(id => !found.has(id));
        throw new NotFoundException(`Seat(s) not found: ${missing.join(', ')}`);
      }

      const blocked = seats.filter(s => s.status === 'BLOCKED' || s.status === 'BOOKED');
      if (blocked.length > 0)
        throw new ConflictException(`Seat(s) ${blocked.map(s => s.seatNumber).join(', ')} are already taken`);

      const seatLabelById = Object.fromEntries(seats.map(s => [s.id, s.seatNumber]));
      const stopTimes = await tx.tripStopTime.findMany({
        where: { scheduleId: dto.scheduleId },
        select: { stationId: true, sequence: true },
      });

      // When no stop times exist, fall back to the schedule's own origin/destination
      // with synthetic sequences so the hold can still be created.
      let effectiveStopTimes = stopTimes;
      if (stopTimes.length === 0) {
        const sched = await tx.trainSchedule.findUnique({
          where: { id: dto.scheduleId },
          select: { originStationId: true, destinationStationId: true },
        });
        if (sched) {
          effectiveStopTimes = [
            { stationId: sched.originStationId, sequence: 0 },
            { stationId: sched.destinationStationId, sequence: 1 },
          ];
        }
      }

      const seqOf = (stationId: string) => effectiveStopTimes.find(s => s.stationId === stationId)?.sequence;
      const reqFrom = seqOf(dto.originStationId);
      const reqTo   = seqOf(dto.destinationStationId);

      if (reqFrom === undefined || reqTo === undefined)
        throw new BadRequestException('Origin or destination station not found');
      if (reqFrom >= reqTo)
        throw new BadRequestException('Origin must come before destination');

      const currentDirection = dto.journeyDirection || JourneyDirection.ONE_WAY;
      const activeHolds = await tx.seatHold.findMany({
        where: { scheduleId: dto.scheduleId, expiresAt: { gt: new Date() } },
        select: { seatIds: true, createdBy: true },
      });

      for (const h of activeHolds) {
        const rawSeatIds = h.seatIds as string[];
        let holdDirection = JourneyDirection.ONE_WAY;
        let holdFrom = 0, holdTo = Number.MAX_SAFE_INTEGER;
        let passengerIds: string[] = [];
        let legUnknown = true;

        try {
          if (h.createdBy?.trimStart().startsWith('{')) {
            const meta = JSON.parse(h.createdBy);
            holdFrom = seqOf(meta.originStationId) ?? 0;
            holdTo = seqOf(meta.destinationStationId) ?? Number.MAX_SAFE_INTEGER;
            holdDirection = meta.journeyDirection || JourneyDirection.ONE_WAY;
            passengerIds = (meta.passengers ?? []).map((p: any) => p.passengerId);
            legUnknown = !meta.originStationId || !meta.destinationStationId;
          }
        } catch { /* ignore */ }

        const legsOverlap = legUnknown || (holdFrom < reqTo && reqFrom < holdTo);
        if (!legsOverlap) continue;

        const directionsConflict = this.checkDirectionConflict(currentDirection, holdDirection);
        if (!directionsConflict) continue;

        for (const { passengerId, seatId } of dto.passengers) {
          if (rawSeatIds.includes(seatId)) {
            throw new ConflictException(`Seat ${seatLabelById[seatId]} is already held for this leg`);
          }
          if (!legUnknown && passengerIds.includes(passengerId)) {
            throw new ConflictException(`Passenger already holds a seat on this journey leg`);
          }
        }
      }

      const bookedSegments = await tx.journeySegment.findMany({
        where: {
          scheduleId: dto.scheduleId,
          seatId: { in: seatIds },
          journey: { status: { in: ['CONFIRMED', 'PENDING_PAYMENT'] } },
        },
        select: { seatId: true, departureStationId: true, arrivalStationId: true },
      });

      for (const seg of bookedSegments) {
        if (!seg.seatId) continue;
        const segFrom = seqOf(seg.departureStationId);
        const segTo   = seqOf(seg.arrivalStationId);
        const overlaps = (segFrom === undefined || segTo === undefined) ? true : segFrom < reqTo && reqFrom < segTo;
        if (overlaps) {
          throw new ConflictException(`Seat ${seatLabelById[seg.seatId]} is already booked for this leg`);
        }
      }

      const holdMeta = {
        originStationId: dto.originStationId,
        destinationStationId: dto.destinationStationId,
        journeyDirection: currentDirection,
        passengers: dto.passengers.map(p => ({ passengerId: p.passengerId, seatId: p.seatId })),
      };

      await tx.seat.updateMany({
        where: { id: { in: seatIds } },
        data: { status: 'HELD' },
      });

      return tx.seatHold.create({
        data: {
          scheduleId: dto.scheduleId,
          passengerId: dto.passengers[0].passengerId,
          seatIds,
          createdBy: JSON.stringify(holdMeta),
          expiresAt,
        },
      });
    });

    return this.enrichHold(hold);
  }

  async getHolds(scheduleId?: string, passengerId?: string) {
    const holds = await this.prisma.seatHold.findMany({
      where: {
        expiresAt: { gt: new Date() },
        ...(scheduleId  ? { scheduleId }  : {}),
        ...(passengerId ? { passengerId } : {}),
      },
      orderBy: { createdAt: 'desc' },
    });
    return Promise.all(holds.map(h => this.enrichHold(h)));
  }

  async getHold(holdId: string) {
    const hold = await this.prisma.seatHold.findUnique({ where: { id: holdId } });
    if (!hold) throw new NotFoundException('Hold not found');
    return this.enrichHold(hold);
  }

  private async enrichHold(hold: any) {
    let originStationId: string | null = null;
    let destinationStationId: string | null = null;
    let passengerSeatMap: { passengerId: string; seatId: string }[] = [];

    try {
      if (hold.createdBy) {
        const raw = hold.createdBy;
        if (typeof raw === 'string' && raw.trimStart().startsWith('{')) {
          const meta = JSON.parse(raw);
          originStationId      = meta.originStationId      ?? null;
          destinationStationId = meta.destinationStationId ?? null;
          passengerSeatMap     = Array.isArray(meta.passengers) ? meta.passengers : [];
        }
      }
    } catch { /* ignore */ }

    const seatIds = hold.seatIds as string[];

    const [schedule, originStation, destinationStation, seats] = await Promise.all([
      this.prisma.trainSchedule.findUnique({
        where: { id: hold.scheduleId },
        include: { train: true, originStation: true, destinationStation: true },
      }),
      originStationId      ? this.prisma.station.findUnique({ where: { id: originStationId } })      : null,
      destinationStationId ? this.prisma.station.findUnique({ where: { id: destinationStationId } }) : null,
      this.prisma.seat.findMany({
        where: { id: { in: seatIds } },
        include: { coach: true },
      }),
    ]);

    let originSequence: number | null = null;
    let destinationSequence: number | null = null;
    if (originStationId && destinationStationId) {
      const stopTimes = await this.prisma.tripStopTime.findMany({
        where: { scheduleId: hold.scheduleId, stationId: { in: [originStationId, destinationStationId] } },
        select: { stationId: true, sequence: true },
      });
      originSequence      = stopTimes.find(s => s.stationId === originStationId)?.sequence      ?? null;
      destinationSequence = stopTimes.find(s => s.stationId === destinationStationId)?.sequence ?? null;
    }

    const seatById = Object.fromEntries(seats.map(s => [s.id, s]));

    const passengers = passengerSeatMap.length > 0
      ? passengerSeatMap.map(({ passengerId, seatId }) => {
          const s = seatById[seatId];
          return {
            passengerId,
            seat: s ? {
              id:         s.id,
              label:      s.seatNumber,
              seatNumber: s.seatNumber,
              coach:      s.coach.number,
              seatClass:  'Standard',
              row:        s.row,
              col:        s.col,
            } : { id: seatId },
          };
        })
      : seatIds.map(seatId => {
          const s = seatById[seatId];
          return {
            passengerId: hold.passengerId,
            seat: s ? {
              id:         s.id,
              label:      s.seatNumber,
              seatNumber: s.seatNumber,
              coach:      s.coach.number,
              seatClass:  'Standard',
              row:        s.row,
              col:        s.col,
            } : { id: seatId },
          };
        });

    return {
      holdId:     hold.id,
      expiresAt:  hold.expiresAt,
      createdAt:  hold.createdAt,
      ttlSeconds: Math.max(0, Math.floor((hold.expiresAt.getTime() - Date.now()) / 1000)),
      schedule: schedule ? {
        id:                   schedule.id,
        trainNumber:          schedule.train.number,
        trainName:            schedule.train.name,
        departureAt:          schedule.departureAt,
        arrivalAt:            schedule.arrivalAt,
        fullRouteOrigin:      schedule.originStation.name,
        fullRouteDestination: schedule.destinationStation.name,
      } : null,
      leg: {
        originStationId,
        originStationName:      originStation?.name ?? null,
        originStationCode:      originStation?.code ?? null,
        originSequence,
        destinationStationId,
        destinationStationName: destinationStation?.name ?? null,
        destinationStationCode: destinationStation?.code ?? null,
        destinationSequence,
      },
      passengers,
    };
  }

  async releaseHold(holdId: string) {
    const hold = await this.prisma.seatHold.findUnique({ where: { id: holdId } });
    if (!hold) throw new NotFoundException('Hold not found');
    await this.prisma.$transaction([
      this.prisma.seat.updateMany({
        where: { id: { in: hold.seatIds as string[] }, status: 'HELD' },
        data: { status: 'AVAILABLE' },
      }),
      this.prisma.seatHold.delete({ where: { id: holdId } }),
    ]);
    return { released: true, holdId };
  }

  // Called right after a booking (PNR) is created, and again on successful payment.
  // Extends the SeatHold(s) covering these seats to the booking's actual payment
  // deadline — the same MIN(createdAt + 2h, departureAt - 30min) window TasksService
  // uses to auto-cancel unpaid bookings — instead of leaving them on the original
  // short seat-selection hold (5 min by default). Without this, the hold could expire
  // while the customer was still on the payment page, and a second customer could
  // hold/book the exact same seat out from under them.
  async confirmSeats(seatIds: string[], now: Date = new Date()): Promise<void> {
    if (seatIds.length === 0) return;

    const holds = await this.prisma.seatHold.findMany({
      where: { seatIds: { hasSome: seatIds } },
      select: { id: true, scheduleId: true, expiresAt: true },
    });
    if (holds.length === 0) return;

    const scheduleIds = Array.from(new Set(holds.map(h => h.scheduleId)));
    const schedules = await this.prisma.trainSchedule.findMany({
      where: { id: { in: scheduleIds } },
      select: { id: true, departureAt: true },
    });
    const departureById = new Map(schedules.map(s => [s.id, s.departureAt]));

    let extended = 0;
    await Promise.all(
      holds.map(async (hold) => {
        const departureAt = departureById.get(hold.scheduleId);
        if (!departureAt) return;
        const deadline = computePaymentDeadline(now, departureAt);
        // Only ever extend forward — never shorten a hold that's already valid longer
        // than the payment deadline would give it (e.g. a second confirmSeats call on
        // the same booking, or a hold that was already extended).
        if (deadline <= hold.expiresAt) return;
        await this.prisma.seatHold.update({ where: { id: hold.id }, data: { expiresAt: deadline } });
        extended++;
      }),
    );

    if (extended > 0) {
      this.logger.log(
        `Extended ${extended} seat hold(s) covering ${seatIds.length} seat(s) to their booking's payment deadline`,
      );
    }
  }

  // Delete the Journey (and its JourneySegments) scoped to this booking.
  async releaseSeats(bookingId: string) {
    await this.prisma.journey.deleteMany({ where: { bookingId } as any });
  }

  async getCoachesWithAvailability(scheduleId: string, originStationId?: string, destinationStationId?: string) {
    const schedule = await this.prisma.trainSchedule.findUnique({
      where: { id: scheduleId },
      select: { originStationId: true, destinationStationId: true },
    });
    if (!schedule) throw new NotFoundException('Schedule not found');

    const assignments = await this.prisma.coachAssignment.findMany({
      where: { scheduleId },
      include: {
        coach: {
          include: {
            seats: { select: { id: true, status: true, seatNumber: true } },
            coachType: { include: { seatClasses: { select: { name: true } } } },
          },
        },
      },
      orderBy: { positionNumber: 'asc' },
    });

    const allSeatIds = assignments.flatMap(a => a.coach.seats.map(s => s.id));
    const effectiveStatuses = await this.resolveEffectiveStatuses(
      scheduleId,
      allSeatIds,
      originStationId ?? schedule.originStationId,
      destinationStationId ?? schedule.destinationStationId,
    );

    return assignments.map(a => {
      const seats = a.coach.seats.filter(s => s.seatNumber && !s.seatNumber.startsWith('-'));
      const totalSeats = seats.length;
      const unavailable = seats.filter(s => {
        const status = effectiveStatuses.get(s.id) ?? (s.status === 'BLOCKED' || s.status === 'BOOKED' ? s.status : 'AVAILABLE');
        return status === 'HELD' || status === 'BOOKED' || status === 'BLOCKED';
      }).length;

      return {
        coachId: a.coach.id,
        coachTypeId: a.coach.coachType?.id ?? null,
        coachNumber: a.coach.number,
        positionNumber: a.positionNumber,
        coachTypeName: a.coach.coachType?.name ?? '',
        seatClasses: a.coach.coachType?.seatClasses.map(sc => sc.name) ?? [],
        totalSeats,
        availableSeats: totalSeats - unavailable,
        heldSeats: seats.filter(s => (effectiveStatuses.get(s.id) ?? (s.status === 'BLOCKED' || s.status === 'BOOKED' ? s.status : 'AVAILABLE')) === 'HELD').length,
        bookedSeats: seats.filter(s => (effectiveStatuses.get(s.id) ?? (s.status === 'BLOCKED' || s.status === 'BOOKED' ? s.status : 'AVAILABLE')) === 'BOOKED').length,
      };
    });
  }

  async autoAssignSeats(scheduleId: string, count: number, seatClassName: string): Promise<string[]> {
    const seats = await this.prisma.seat.findMany({
      where: {
        coach: { assignments: { some: { scheduleId } } },
        status: 'AVAILABLE',
        seatNumber: { not: '' },
        NOT: { seatNumber: { startsWith: '-' } },
      },
      orderBy: [{ coach: { number: 'asc' } }, { row: 'asc' }, { col: 'asc' }],
    });

    if (seats.length < count) {
      throw new ConflictException(`Only ${seats.length} seats available, requested ${count}`);
    }

    const assigned = this.findContiguousSeats(seats, count);
    return assigned.map((s) => s.id);
  }

  private findContiguousSeats(seats: any[], count: number): any[] {
    if (count === 1) return [seats[0]];

    const grouped = new Map<string, any[]>();
    for (const seat of seats) {
      const key = `${seat.coachId}-${seat.row}`;
      if (!grouped.has(key)) grouped.set(key, []);
      grouped.get(key)!.push(seat);
    }

    for (const rowSeats of grouped.values()) {
      if (rowSeats.length >= count) {
        return rowSeats.slice(0, count);
      }
    }

    return seats.slice(0, count);
  }

  async exportSeatsCSV(scheduleId: string): Promise<string> {
    const assignments = await this.prisma.coachAssignment.findMany({
      where: { scheduleId },
      include: { coach: { include: { seats: { orderBy: [{ row: 'asc' }, { col: 'asc' }] } } } },
    });
    const rows = ['coachId,coachLabel,row,col,seatNumber,kind,status,premiumFeeMinor'];
    for (const a of assignments) {
      for (const seat of a.coach.seats) {
        rows.push(`${a.coach.id},${a.coach.number},${seat.row},${seat.col},${seat.seatNumber},${seat.kind},${seat.status},${seat.premiumFeeMinor}`);
      }
    }
    return rows.join('\n');
  }

  async previewSeatsCSV(csvContent: string): Promise<{ valid: number; invalid: number; errors: string[] }> {
    const lines = csvContent.trim().split('\n').slice(1);
    const errors: string[] = [];
    let valid = 0;
    let invalid = 0;

    for (let i = 0; i < lines.length; i++) {
      const parts = lines[i].split(',');
      if (parts.length < 8) {
        errors.push(`Line ${i + 2}: Invalid format`);
        invalid++;
        continue;
      }
      const [coachId, , row, col, seatNumber] = parts;
      if (!coachId || !row || !col || !seatNumber) {
        errors.push(`Line ${i + 2}: Missing required fields`);
        invalid++;
        continue;
      }
      valid++;
    }

    return { valid, invalid, errors: errors.slice(0, 10) };
  }

  async importSeatsCSV(scheduleId: string, csvContent: string, commit: boolean): Promise<{ imported: number; errors: string[] }> {
    const lines = csvContent.trim().split('\n').slice(1);
    const errors: string[] = [];
    let imported = 0;

    if (!commit) {
      return { imported: 0, errors: ['Preview mode'] };
    }

    for (let i = 0; i < lines.length; i++) {
      try {
        const parts = lines[i].split(',');
        const [coachId, , row, col, seatNumber, kind, status, premiumFeeMinor] = parts;

        await this.prisma.seat.upsert({
          where: { coachId_row_col: { coachId, row: parseInt(row), col } },
          update: {
            seatNumber,
            kind: kind as any,
            status: status as any,
            premiumFeeMinor: parseInt(premiumFeeMinor) || 0,
          },
          create: {
            coachId,
            row: parseInt(row),
            col,
            seatNumber,
            kind: kind as any,
            status: status as any,
            premiumFeeMinor: parseInt(premiumFeeMinor) || 0,
          },
        });
        imported++;
      } catch (err) {
        errors.push(`Line ${i + 2}: ${err instanceof Error ? err.message : String(err)}`);
      }
    }

    return { imported, errors: errors.slice(0, 10) };
  }

  async blockSeat(seatId: string, reason: string) {
    const seat = await this.prisma.seat.findUnique({ where: { id: seatId } });
    if (!seat) throw new NotFoundException('Seat not found');

    await this.prisma.seat.update({ where: { id: seatId }, data: { status: 'BLOCKED' } });
    await this.prisma.seatBlock.create({ data: { seatId, reason, blockedBy: 'system' } });
    await this.auditService.log({ action: 'UPDATE', entityType: 'Seat', entityId: seatId, newData: { status: 'BLOCKED', reason } });
    return { blocked: true, seatId, reason };
  }

  async unblockSeat(seatId: string) {
    const seat = await this.prisma.seat.findUnique({ where: { id: seatId } });
    if (!seat) throw new NotFoundException('Seat not found');

    await this.prisma.seat.update({ where: { id: seatId }, data: { status: 'AVAILABLE' } });
    await this.prisma.seatBlock.deleteMany({ where: { seatId } });
    await this.auditService.log({ action: 'UPDATE', entityType: 'Seat', entityId: seatId, newData: { status: 'AVAILABLE' } });
    return { unblocked: true, seatId };
  }

  async setMaintenance(seatId: string, reason: string) {
    const seat = await this.prisma.seat.findUnique({ where: { id: seatId } });
    if (!seat) throw new NotFoundException('Seat not found');
    if (seat.status === 'BOOKED') throw new BadRequestException('Cannot set a booked seat to maintenance');
    await this.prisma.seat.update({ where: { id: seatId }, data: { status: 'UNDER_MAINTENANCE' as any } });
    await this.prisma.seatBlock.create({ data: { seatId, reason: `MAINTENANCE: ${reason}`, blockedBy: 'system' } });
    return { maintenance: true, seatId, reason };
  }

  async clearMaintenance(seatId: string) {
    const seat = await this.prisma.seat.findUnique({ where: { id: seatId } });
    if (!seat) throw new NotFoundException('Seat not found');
    await this.prisma.seat.update({ where: { id: seatId }, data: { status: 'AVAILABLE' as any } });
    await this.prisma.seatBlock.deleteMany({ where: { seatId } });
    return { maintenance: false, seatId };
  }

  async removeSeat(seatId: string) {
    const seat = await this.prisma.seat.findUnique({ where: { id: seatId } });
    if (!seat) throw new NotFoundException('Seat not found');
    if (!seat.seatNumber || seat.seatNumber.startsWith('-')) throw new BadRequestException('Seat already removed');

    // Mark as removed, then renumber all active seats in the coach
    await this.prisma.seat.update({
      where: { id: seatId },
      data: { seatNumber: `-${seat.seatNumber}` },
    });

    await this.renumberCoachSeats(seat.coachId);
    await this.auditService.log({ action: 'DELETE', entityType: 'Seat', entityId: seatId, oldData: { seatNumber: seat.seatNumber, coachId: seat.coachId } });
    return { removed: true, seatId, originalSeatNumber: seat.seatNumber };
  }

  async undoRemoveSeat(seatId: string) {
    const seat = await this.prisma.seat.findUnique({ where: { id: seatId } });
    if (!seat) throw new NotFoundException('Seat not found');
    if (!seat.seatNumber || !seat.seatNumber.startsWith('-')) {
      throw new BadRequestException('Seat is not removed');
    }

    // Restore with a temporary placeholder number, then renumber
    await this.prisma.seat.update({ where: { id: seatId }, data: { seatNumber: `__restore__${seatId}` } });
    await this.renumberCoachSeats(seat.coachId);

    const restored = await this.prisma.seat.findUnique({ where: { id: seatId } });
    return { restored: true, seatId, seatNumber: restored?.seatNumber };
  }

  /**
   * Renumbers all active (non-removed) seats in a coach sequentially starting from 1,
   * ordered by row then col. Removed seats (prefixed with "-") keep their slot but
   * are excluded from the numbering sequence so numbers remain continuous.
   */
  private async renumberCoachSeats(coachId: string): Promise<void> {
    const allSeats = await this.prisma.seat.findMany({
      where: { coachId },
      orderBy: [{ row: 'asc' }, { col: 'asc' }],
      select: { id: true, seatNumber: true },
    });

    const activeSeats = allSeats.filter(
      (s) => s.seatNumber && !s.seatNumber.startsWith('-') && !s.seatNumber.startsWith('__restore__'),
    );

    await Promise.all(
      activeSeats.map((s, idx) =>
        this.prisma.seat.update({
          where: { id: s.id },
          data: { seatNumber: String(idx + 1) },
        }),
      ),
    );
  }

  // Runs every minute, but is also safe to call on-demand (e.g. right after a hold's
  // TTL is read back to the client) — expiresAt/now are both absolute UTC instants
  // (Date objects, not wall-clock strings), so this is correct regardless of the
  // server's or a client's local timezone; there's no wall-clock parsing involved.
  @Cron(CronExpression.EVERY_MINUTE)
  async expireHolds() {
    try {
      const result = await this.expireHoldsCore();
      if (result.expiredHolds > 0) {
        this.logger.log(
          `Expired ${result.expiredHolds} hold(s): released ${result.releasedSeatIds.length} seat(s), ` +
          `skipped ${result.skippedSeatIds.length} still held by another active hold on the same schedule`,
        );
      }
    } catch (error) {
      // A failed run must not crash the process or silently go unnoticed — the next
      // scheduled run one minute later will retry the same (still-expired) holds,
      // since nothing here is deleted/updated until the queries above succeed.
      this.logger.error('Failed to expire seat holds', error instanceof Error ? error.stack : error);
    }
  }

  async expireHoldsCore(now: Date = new Date()): Promise<{
    expiredHolds: number;
    releasedSeatIds: string[];
    skippedSeatIds: string[];
  }> {
    const expired = await this.prisma.seatHold.findMany({
      where: { expiresAt: { lt: now } },
      select: { id: true, scheduleId: true, seatIds: true },
    });
    if (expired.length === 0) {
      return { expiredHolds: 0, releasedSeatIds: [], skippedSeatIds: [] };
    }

    // Still-active holds — scoped per (scheduleId, seatId), not just seatId. The same
    // physical Seat row is reused across every recurring date a coach runs, so the
    // same seatId legitimately appears in unrelated holds for other schedules; without
    // this scoping, an unrelated active hold on a DIFFERENT schedule would wrongly
    // block release of a seat whose hold expired on THIS schedule, leaving it stuck at
    // status 'HELD' indefinitely.
    const activeHolds = await this.prisma.seatHold.findMany({
      where: { expiresAt: { gte: now } },
      select: { scheduleId: true, seatIds: true },
    });
    const stillHeldKeys = new Set(
      activeHolds.flatMap(h => (h.seatIds as string[]).map(seatId => `${h.scheduleId}:${seatId}`)),
    );

    const releasedSeatIds = new Set<string>();
    const skippedSeatIds = new Set<string>();
    for (const hold of expired) {
      for (const seatId of hold.seatIds as string[]) {
        if (stillHeldKeys.has(`${hold.scheduleId}:${seatId}`)) {
          skippedSeatIds.add(seatId);
        } else {
          releasedSeatIds.add(seatId);
        }
      }
    }

    if (releasedSeatIds.size > 0) {
      await this.prisma.seat.updateMany({
        where: { id: { in: Array.from(releasedSeatIds) }, status: 'HELD' },
        // heldUntil is cleared alongside status — leaving a stale (past) heldUntil on an
        // AVAILABLE seat is stale data that any future code reading heldUntil directly
        // (instead of re-deriving availability live) would misinterpret.
        data: { status: 'AVAILABLE', heldUntil: null },
      });
    }

    await this.prisma.seatHold.deleteMany({ where: { expiresAt: { lt: now } } });

    return {
      expiredHolds: expired.length,
      releasedSeatIds: Array.from(releasedSeatIds),
      skippedSeatIds: Array.from(skippedSeatIds),
    };
  }
}